1. Field of the Invention
This invention relates to tuner mechanisms, more particularly to tuner mechanisms of the type known as "push button, press-to-lock" tuner mechanisms.
2. Description of the Prior Art
A known push button, press-to-lock tuner mechanism includes reactive circuit components, e.g. an assembly of coils, the reactances of which are altered to vary the frequency of tuned circuits in an associated radio receiver, e.g. an automobile radio receiver, to enable selection of a desired wavelength. The reactances are mechanically varied, in the case of the coils the inductances being varied by moving ferromagnetic cores into and out of the coils. The tuner mechanism includes means for infinitely varying the inductances, such means comprising a tuning spindle protruding through a control panel of the mechanism and minimal-backlash transmission means interconnecting the spindle and cores and arranged to move the cores into and out of the coils with rotation of the tuning spindle.
The known mechanism also includes a member known as a "treadle bar". The treadle bar may comprise two like rods of equal diameter which are spaced apart by (and attached to) end plates to form an elongate rectangular structure mounted so that its longitudinal axis is horizontal and so that it is pivotable about such axis. Rotation of the treadle bar about this axis gives a range of angular positions to the rods on either side of a central position in which the rods lie in a vertical plane. The treadle bar is connected to or forms part of said transmission means so that it is rotated about its longitudinal axis with roation of the tuning spindle.
A plurality of push buttons are also provided, each for enabling the user to select a respective, associated wavelength merely by pressing the button, i.e. without rotating the tuning spindle. Each button is provided with an actuating member having a cam thereon. When the button is pushed inwardly from a rest position towards which the associated actuating member is biassed, a pair of surfaces on the cam contact the rods of the treadle bar and rotate the treadle bar about its axis to a position determined by the orientation of the cam, and therefore move the ferromagnetic cores to corresponding positions.
The actuating members and push buttons are arranged so that the wavelength or frequency selected by pushing each button can be selected at will. To change the wavelength selected by pushing any one button, the new wavelength is selected by using the tuning spindle. The button is then pulled outwardly of the rest position i.e. outwardly with respect to the associated actuating member, thereby freeing the associated cam to rotate. The button is then pushed inwardly past the rest position. The cam contacts the treadle bar and, since the cam is free to rotate, it adopts a position determined by the position of the treadle bar, which position was set by using the tuning spindle. The cam and actuating member are then held stationary by abutment with the treadle bar and further inward pressure on the button therefore causes the button to move back inwardly with respect to the acutating member to its original position, thereby locking the cam in its new position. Consequently, whenever the button is subsequently used, it moves the treadle bar to the position which was selected by movement of the tuning spindle to select the desired wavelength.
The above-described type of tuner mechanism is subject to the disadvantage that, since it employs a treadle bar mounted and arranged as described, it must be at least high enough to accommodate the treadle bar when it lies in a vertical plane.